Polarized infrared spectroscopic study on changes in molecular orientationand interaction during phase transitions of a ferroelectric liquid crystalwith a naphthalene ring

Temperature-dependent polarized infrared spectra were measured over the tem perature range 105-30 degreesC for a ferroelectric liquid crystal with a na phthalene ring (FLC-1) in the isotropic, smectic A (SmA), and chiral smecti c C (SmC*) phases to investigate its molecular conformation, interactions, and alignment in each phase. It has been found, from the temperature-depend ent spectral changes in the 1610-1600 cm(-1) region, that the degree of twi st between the naphthalene and benzene rings of FLC-1 changes with temperat ure. The peak intensity of the band at 1606 cm(-1) containing contributions from both the benzene and naphthalene ring stretching modes begins to decr ease, not suddenly but gradually, upon going from the SmA phase to the SmC* phase, suggesting that the molecular orientation of the two rings changes gradually between the two phases. The frequencies of two CH2 stretching ban ds suggest that the disorder of the alkyl chain of FLC-1 is similar for the liquid crystal phase and the isotropic liquid phase. The splitting of the core C=O stretching band indicates that the resonance system consisting of the benzene ring and the C=O group in the core part of FLC-1 is involved in two kinds of intermolecular interaction between adjacent molecules in the liquid crystal phase.